Confused about Azure Functions premium plan pricing

I've read the other two issues related to this that I found but neither seems to give a clear explanation, or they get derailed around pre-warming mechanics, or at least don't answer the question of how much it costs.

From my understanding from reading the official docs is that a premium Fn has a fixed monthly cost for the instance(s), plus the usage cost on top of that. This instance cost is not baked into the advertised usage costs; it's additional and separate.

So, for example, for a simple function that needs one instance and runs for ~50 ms and uses 128 MB of memory (or less), <1M executions, everything falls under the free grant. Would one only pay that fixed warm instance cost for the single instance? If so, how much is that, or how does one calculate that cost?

The pricing page currently says $0.16 vCPU/hour, which I think is roughly $0.00004/sec. 50 ms * 1M = 50,000 sec * .00004 = $2/mo? Memory (128 MB) comes out to about $0.02/mo, if my calculations are correct. So does that mean it's <$3/mo? Or is it free since it's small? Or is it the cost of a single warm instance? Or the instance cost plus $3/mo? :)